Signaling system



Oct. 6, 1936. c. s. DEMARVEST ET AL SIGNALING SYSTEM Filed Jan. 2., 1936 12 Sheets-Sheet 1 0 5mm H mmfi M m NW N C Oct. 6, 1936. c. s. DEMARESTET AL S IGNALING SYSTEM Filed Jan. 2, 1936 12 Sheets-Sheet 2 I wu INVENTORS BY JZFwZW L ATTORNEY Oct. 6, 1936. c s, M T ET AL 2,056,347

SIGNALING SYSTEM 12 Sheets-Sheet 3 Filed Jan. 2, 1936 BY JFRwdcZL c ATTORNEY Oct. 6, 1936- c. s. DEMAREST ET AL SIGNALING SYSTEM Filed Jan. 2, 1936 12 Sheets-Sheet 4 8 5 43% T 3R8 3m Oct. 6, 1936- c. s. DEMAREST ET AL SIGNALING SYSTEM Filed Jan. 2, 1936 12 Sheets-Sheet 5 kw QM mkw INVENTORS C. $.fie1mams2f 6% BY Jfifloadclyf ATTORNEY Oct. 6, 1936. -c. s. DEYMARESTIET AL 2,056,347

S IGNALING SYSTEM Filed. Jan. 2, 1936 12 Sheets-Sheet 7 Gasfi/led 7am 80 U J ii,

INVENTORS CASZZZeM zar/ e nFZ BY J]? add;

Q. ATTORNEY Oct. 6, 1936.

c. s. DEMAREST ET AL 2,056,347

SIGNALING SYSTEM Filed Jan. 2, 1936 12 Sheets-Sheet 8 6-515 ilt'led 4 ATTORNEY Oct. 6, 1936. c. 's. DEMAREST AL I 2,0

S IGNALING SYSTEM Filed Jan. 2, 1936 12 Sheets-Sheet 9 J) Ea 5 1 I 465- W 5Z 1 l BET INVENTORS Sfiewaareszpf? c. ATTORNEY Oct; 6, 1935. c. S. DEMAREST' ET AL S IGNALING SYS TEM Filed Jan. 2, 1936 12 Sheets-Sheet 10 INVENTORS 6'. {SD/87060676886. BY JBZZadcZLfl ATTORNEY 5711936. c. s; 'DEMAREST- AL I I 2,056,347 I SIGNALING SYSTEM Filed Jan. 2, 1936 12 Sheets-Sheet 11 772' 17 I 760' mamas 769'] 7271' 555 fiasflaed L v t A 8807 k I 8802' t: I I Y v 8803' C 8804 a v 4 KW, INVENTORS ATTORN EY Oct. 6,1936. 0 c. s. DEMARET ET AL 2,056,347 I SIGNALING'SYSTEM Filed Jan 2, 1956 I 12 Sheets-Sheet 12 Patented Oct. 6, 1936 UNITED STATES PATENT OFFICE SIGNALING SYSTEM Application January 2, 1936, Serial No. 57,266

23 Claims.

This invention relates to transmission systems and more particularly to improved means for signaling over such systems and is a continuation in part of our application Serial No. 4583, filed February 1,1935.-

As the invention is particularly adapted for use in signaling Over certain types of telephone circuits, it will be specifically described herein with respect to the type of circuit termed a through two-way supervision toll circuit. In the through two-way supervision toll circuit, the outgoing toll operator has complete supervision of the whole circuit. All supervisory signals are transmitted from both the calling and the called party to the outward toll operator. In this type of circuit the supervisory signals are transmitted through an intermediate point of a built-up connection without the aid of an operator. While the invention is described with respect'to this type of toll circuit, it is understood that it is for the purpose of illustration only and that the arrangements of the invention may be used with other types of transmission systems.

The signaling and control arrangements in toll circuits heretofore used employ direct current, low frequency alternating current, or voice frequency alternating current or any combination of these which may be necessary to operate electromagnetic relays and other devices requiring mechanically moving parts for contactmaking and contact-breaking devices either directly or with the aid of associated apparatus. Such apparatus requires mechanical adjustment which sometimes necessitates considerable maintenance in practice. The speed of operation of mechanical devices is limited by the weight of the moving parts or by the time required to build up a magnetic field in the electromagnetic field. This may limit the application of such devices because of the slowness of operation. In some cases marginal operation is employed to perform certain operations. The number of margins which are permissible when electromagnetic devices are employed is limited. It is difficult to devise electromagnetic devices which will operate successfully at any but relatively low frequencies. This factor limits the possible use of various frequencies as means of signaling overtelephone circuits, 'The signaling and control arrangements now available for telephone systems, therefore, are somewhat limited in the number of variables which may be employed to perform various necessary functions In the arrangements of this invention, gasfilled discharge tubes together with circuits design-ed therefor are utilized to replace electromagnetic devices. Gas-filled discharge tubes are capable of response to currents of relatively high frequencies as well as low frequencies and direct current. Accordingly, the combination of gasfilled tubes and circuit arrangements therefor result in a signaling system applicable to transmission circuits which is superior to the relay arrangements of the prior art, since the number of frequencies which may be employed and, consequently, the variety of functions obtainable is greatly increased. Moreover, in accordance with this invention, the gas-filled tubes and circuit arrangements therefor are of such design that the tube can be caused to operate or release as the circuit may require by means of the application of carrier frequency, alternating current, alternating currents of lower frequency or direct currents of the proper polarity. The direct current may be supplied by either the primary or secondary cells through resistance units or alternating current which has been rectified by means of rectox units, vacuum tube or gas-filled rectifiers or by any other rectifying device, several of which are well known in the art. Furthermore, in accordance-with the arrangements of this invention, more precise and constant specific time of operation is obtained through the use of gasfilled tubes and their associated circuits than can be obtained by using a system of electromagnetic relays. Also, the gas-filled tube circuits are capable of being faster acting than the electromagnetic equipment and the gas-filled tube, and circuittherefor, adapts itself readily to marginal operation.

The invention may be more fully understood from the following description together with the accompanying drawings, in the Figures 1, 2, 3, 4, 6, 7, 9, 10, 11, 1, 5', 8', 9, 10', 11 and 12' of which are shown circuit diagrams embodying one form of the invention. Figure 1 is a circuit diagram showing a local subscribers line connecting the subscriber to the local ofiice. In the drawings Fig. 2 should be placed to the right of Fig. 1. Fig. 2 shows a cord circuit for the operator at the local office. In the drawings Fig. 3 is placed to the right of Fig. 2. Fig. 3 shows a recording trunk for interconnecting the local olfice with a toll office. In the drawings Fig. 4 is placed to the right of Fig. 3. Fig. 4 shows a cord circuit for the operator at the toll ofiice. Figs. 6 and '7 show a toll switching trunk when Fig. '7 is placed to the right of Fig. 6. This toll switching trunk may be used to establish a connection between the local subscribers line, such as shown in Fig. 1, and a toll operators cord circuit, such as shown in Fig. 4. Figs. 9, 10 and 11 should be placed in the drawings so that Fig. 9 is to the right of Fig. 4. Fig. 10 is to the right of Fig. 9, and Fig. 11 is to the right of Fig. 10. When so placed Figs. 9, 10 and 11 show certain details of the terminal equipment associated with a toll line of the through two-way supervision type. At the distant end of the toll line there would be the apparatus shown in Figs. 11', 10', 9' and 12', with Fig. 10' placed to the right of Fig. 11', with Fig. 9' placed to the right of Fig. 10' and with Fig. 12 placed to the right of Fig. 9'. As Figs. 9', 10' and 11' are in many respects identical with Figs. 9, 10 and 11, similar reference characters with the added designation prime have been used in Figs. 9, 10 and 11 to indicate like parts with respect to Figs. 9, 10 and 11. Fig. 8' in the drawings should be placed to the right of Fig. 12. Fig. 8 shows the details of a toll switching trunk utilized to connect the toll line to the distant subscribers line which is shown in Fig. 1'. If the toll call were initiated from the subscribers line shown in Fig. 1', a local cord circuit, a recording trunk, a toll operators cord circuit and a toll switching trunk, such as shown respectively, in Figs. 2, 3, 4, 6 and 7, would be provided at the distant end of the line. However, as these circuits would be identical with those shown at the other end of the line they have not been illustrated. If the call is to be completed through an automatic exchange the arrangements of Fig. would be used in place of those of Figs. 8 and 1' and Fig. 5' would be placed to the right of Fig. 12'.

If a call is to be completed over a through two-way supervision toll circuit, the local A operator answers the call in a manner similar to that described above and reaches the toll operator over a two-wire recording trunk. After the toll operator learns the destination of the call she plugs into an outgoing through twoway supervision toll switching trunk interconnecting the outward toll operator to the B board at the local office of the calling subscriber. This lights a. lamp in front of the B operator. The toll operator instructs the local B operator to go into the subscriber's line jack over the busy test. The subscriber is now connected to the toll operator by means of the outgoing through two-way supervision toll switching trunk. The toll operator then pulls down from the two-wire recording trunk, thus giving a disconnect signal to the local A operator who disconnects the subscribers cord from both the subscribers line and the two-wire recording trunk. The toll operator also selects the proper toll circuit and plugs into this circuit with the toll cord. When she plugs into the toll circuit, a lamp is lighted automatically before the incoming toll operator at the distant end. The distant toll operator determines the destination of the call and selects the proper incoming through two-way supervision toll switching trunk interconnecting the inward toll operator to the local oflice of the called subscriber. She then plugs into this trunk with the plug terminated end of the toll line instead of with her cord circuit. Alamp then appears in front of the local B operator who answers the call. Having received the called subscribers number, she plugs into the proper subscribers line jack. This operation automatically starts the subscribers bell ringing. When the subscriber answers, the off-hook signal caused by lifting the receiver from the switch is sent back to the outgoing toll operator who controls the entire circuit. All switchhook signals are transmitted back to this outward toll operator. When either subscriber hangs up, a light appears before the outward toll operator. She then disconnects from the toll circuit which causes a light to appear before the inward toll operator, who disconnects the toll line from the incoming through two-way supervision toll switching trunk. This operation sends a disconnect signal to the local B operators position and she disconnects from the called subscribers line. When the outward toll operator disconnects from the outgoing through two-way supervision toll switching trunk, a light appears at the local B operators position and she disconnects the subscriber from the circuit. In the through two-way supervision toll circuit it is necessary to select a special jack if the circuit is to be built up of more than one toll circuit. To function on a built-up connection, the equipment is so designed that only disconnect signals are received at the intermediate positions. Hence, it is not necessary for the outward toll operator to clear the circuit as in the previously described case.

In the following detailed description of the invention the word operate or derivatives thereof will be used hereafter to indicate the process which takes place within the gas-filled tube when the gas contained inside the bulb ionizes and an arc is established from the oathode to the anode. The word release or derivatives thereof will be used hereafter in the description of this invention to indicate the extinction of the arc and the return of the gas to a deionized condition. Each of the gas-filled tubes in this invention has a protective resistance I in the plate circuit of the tube. This protective resistance is used to limit the current in the plate circuit to a suitable or a safe value. Furthermore, each gas-filled tube has a protective resistance 2 in the grid circuit in order to prevent the grid current of the tube from becoming excessive. Since these resistances are to be found associated with every tube, no further mention will be made of their purpose.

The type of gas-filled tube illustrated herein is of the heater type and the heater power is shown supplied by means of direct current. It is understood in this invention that the cathode is not necessarily of the heater type and the power supply is not limited to direct current. Furthermore, the gas-filled tube may be of the cold cathode type, under which conditions no heater nor heater power would be required, and in which case a glow discharge rather than an arc discharge might be utilized.

The types and characteristics of the gas-filled tubes used in this invention will be varied and numerous and each gas-filled tube employed will be of the type and have the characteristics which are essential and necessary to perform the functions which are required of the tube by the use to which it is specifically put.

One type of tube may be of such physical dimensions that it is capable of being mounted in the switchboard in front of the operator. The gas content of this tube is of such a nature and pressure that a visual glow is present when thetube is operating. However, this type of tube may be used to give a visual indication or to perform some electrical function such as the completion of a circuit. This type of gas-filled tube will be referred to in this description as a combined lamp and relay.

Another type of tube has five electrodes contained within the envelope. The cathode, grid and anode perform the same functions as in the three-element tube. In addition to these elements are two probes or plates. When the tube is in the non-operate or release condition, the resistance between these two probes or plates is very high but when the tube operates and a bias slightly positive with respect to the anode is applied to the probes the resistance between these two probes and the cathode, or between the probes is relatively low. Hence, by properly connecting such a tub-e in a circuit,-the circuit may be completed through these probes or plates. This type of tube will be referred to in this description as a five-element tube.

The other types of tubes employed in this invention are of such physical characteristics and have such gas and gas pressure within the envelope as to meet the requirements which are set up by the circuit conditions.

In the embodiment of the invention described herein, certain gas-filled tubes are arranged for self-quenching by means of an alternating potential applied to the anode circuit from a separate source of alternating current. It is of course, within the scope of this invention toapply other quenching means to such tubes as may require the same in the practice of this invention. For example, one of the aforesaid tubes may be arranged in a self-oscillatory circuit in such a manner that the plate current is interrupted once for each cycle of the operation. It would also be possible to provide auxiliary quenching tubes in such a manner that the discharge would be transferred from one of the main tubes to the auxiliary tube when required, or where tubes are used alternately, from one tube to the other.

Certain gas-filled tubes described in this invention are so connected as to be associated with an auxiliary circuit. Connection is made to these auxiliary circuits through a transformer connected in the plate circuit of certain gas-filled tubes. The words auxiliary circuit are taken to mean such equipment as may not be required if the telephone circuit is to include the connections required for connecting together and giving service to only two subscribers, one at each end of the toll connection or local connection. This auxiliary circuit equipment would be necessary if more than the above mentioned subscribers were to be served. Certain of these auxiliary circuits may also be used in connection with dialing. It is proposed in this description to indicate a method or methods of connecting such auxiliary equipment to the herein described telephone circuit.

Figure 1 is the subscribers line circuit. Gasfilled tube T1 may be a combined lamp and relay. The operation of tube T1 is under the control of the subscribers switchhook and tube T2 which is controlled by the sleeve circuit of jack I4, 25 or 26. When the subscriber lifts the receiver 3 from the switchhook 4, the subscribers line is short-circuited through one of the coils of the induction coil 6 and the telephone transmitter 5. This short-circuit on the line applies the positive potential of battery 7 to the grid of tube T1. The applied potential is of such a polarity as to cause the tube to operate. Tube T1 is normally held released by the negative potential of battery 8 applied to the grid of tube T1 through the resistance 9. The plate of tube T1 is supplied with an alternating potential by generator I through transformer I I. The operation of the tube T1 operates a visual signal to the operator and also allows plate current to flow in the plate circuit of the tube. This current induces a voltage in the secondary of transformer I2 which supplies an auxiliary circuit I3, the purpose of which has been discussed previously. Anti-resonant circuits 2i and 22 consisting of suitable coils and condensers are placed in the input circuit of tube T1 to prevent the alternating current which is supplied to the plate of the tube from being fed back into the telephone line. When the local A operator answers the call, she plugs into the subscribers line jack I4. This applies negative battery to the sleeve of the jack. The potential drop across resistance I in the sleeve circuit is such that tube T2 operates. When tube T2 opcrates, potential is supplied to rectifier I9 by transformer IS. The plate supply of tube T2 is supplied by alternator II through transformer I8. Tube T2 is held normally unoperated by a negative potential supplied by battery 2E. Unidirectional current supplied by rectifier IS flows through filter 23 to resistance 24. The potential drop across resistance 2 3 is in such a direction as to apply the proper polarity to the grid of tube T1 to cause it to release, thus extinguishing the visible glow. Whenever a cord is plugged into any of the subscribers line jacks, I4, 25 or 26, switchhook signals from the subscriber are transferred to the cord circuit and do not cause tube T1 to operate. Jacks 25 and 26 are at inward positions or at the local B operators position and the insertion of a plug in these jacks causes tube T2 to operate and function in the circuit as described above. When the subscriber hangs the receiver 3 on hook 4, the short-circuit is removed from the subscribers line and the potential of battery 7 is removed from the grid of tube T1. Hence, when the cord is pulled out of either jack, is, 25 or 26, tube T1 will not operate and no visible signal is given to the local A operator by tube T1. Should a cord be pulled out of either jack I4, 25 or 26, before the subscriber has placed his receiver on the hook, tube T1 would operate and a visual signal would appear before the local A operator.

Fig. 2 is the local operators cord circuit which is available to the local A operator. The subscribers cord circuit is used to answer calls from the calling subscriber and connect the subscriber to the toll operator if the call is to be a toll call. Incoming calls are answered by inserting plug 2'! into the subscribers line jack. This operation completes the sleeve circuit of the plug, thus allowing a current to flow from battery 29 through resistance 28. The completion of the sleeve circuit applies a negative potential to the grid of tube T3 of such a value that the tube is released. Tube T2 is normally held operated by the positive potential of battery 30 being applied to the grid of the tube. Alternating potential from generator 3! is applied to the plate of tube T3 through transformer 32. When tube T3 is operated, an alternating potential is applied to rectifier 33 through transformer 34. The unidirectional voltage from rectifier 33 passes through filter 35 and is applied to resistance 36. The potential applied across resistance 36 is in such a direction as to oppose the potential supplied by battery 31 to the grid of tube T4. The potential supplied to the grid of tube T4 from battery 31 is applied thereto through resistances 42 and 36. Tube T4 is accordingly normally released. When the subscribers cord is plugged into a line jack tube T3 will release as heretofore pointed out and this will tend to cause tube T4 to operate. However, this operation of tube T4 at this time will be prevented if the subscribers receiver is oiT the hook as will be pointed out hereinafter. The tube T4 may be a combined lamp and relay and is so placed as to be visible to the operator. The alternating potential for tube T4 is supplied by generator 38 through transformer 39. A transformer is provided to connect the subscribers cord circuit shown to auxiliary apparatus, the purpose of which has been discussed above. When the subscribers receiver is off the hook, current from battery 40 is supplied to the subscribers line through the repeating coil 4|. This current flows through resistance 42 in such a direction that potential drop across this resistance is in opposition to the potential applied to the grid by battery 31 and hence will cause a negative potential to be applied to the grid of tube T4 thus releasing the tube. Antiresonant circuits 43 are employed to prevent the alternating potential which is applied to the plate of tube T4 from feeding back into the subscribers line circuit. When the subscriber places the receiver on the hook, current ceases to flow through resistance 42 and tube T4 will operate, thus operating a visual signal to the operator that the subscriber has completed the call. When the operator pulls plug 2'1 out of the line jack, tube T3 operates due to the ceasing of the current flow through resistance 28. When tube T3 operates, a potential is applied across resistance 36 in such a direction as to cause tube T4 to be released. The tubes T5 and To and the equipment associated with them perform in a manner substantially similar to that described immediately above for tubes T3 and T4. This will be pointed out in more detail hereinafter. Key 44 is the key by which the operator can connect her telephone to the line circuit. The operators telephone set and associated equipment are connected at 45. Key 46 is a ringing key to apply ringing current to the subscribers line should the A operator desire to call a subscriber. Condensers 4! are used to send audible ringing current back to the calling subscriber.

Fig. 3 is the two-wire recording trunk which connects the local A operator to the toll operator. This is the trunk over which information is passed from the calling subscriber through the local operator to the toll operator. The trunk is not used to complete the call but the toll operator reaches the calling subscriber over a different type of trunk and the calling subscriber communicates with the called subscriber over the last mentioned trunk but not over a two-wire recording trunk. Signals are transmitted over this trunk only from the local A operator to the toll operator.

The local A operator reaches the toll operator by inserting the plug of the subscribe-rs cord circuit into jack 48. Resistance 49 completes the sleeve circuit of this jack to ground. The plug of a subscribers cord circuit is so wired that the tip has a positive and the ring a negative potential on it. The positive potential applied to the tip of the trunk places a positive potential on the grid of tube T600 causing it to operate. Tube T600 may be the type of combined lamp and relay which has been referred to previously. Tube T600 is normally held released by the potential of battery 5|! applied to the grid of the tube through resistance 5|. The plate potential of tube T600 is supplied by generator 52 through transformer 53. A transformer is used to connect this circuit with auxiliary apparatus. Antiresonant circuits 56 prevent the alternating potential applied to the plate of the tube from going out to the line. When tube T600 operates, there is a visual indication to the toll operator that a call is Waiting on that trunk. She inserts the plug of a toll cord into the jack 57.

The sleeve circuit of jack 5! contains inductances 58 and resistances 59, 60 and 6|. When the plug of the toll operators cord circuit of Fig. 4; is inserted into the line jack 51, current flows from battery 293 through resistance 6|] in such a direction as to apply a positive potential to the grid of Tube T7, causing it to operate. Tube T7 is held normally released by the negative potential supplied to the grid of this tube by battery 68. Generator 62 supplies the alternating plate potential of the tube through transformer 63. When the tube operates, alternating current is applied to rectifier 64 through transformer 65. The unidirectional current from rectifier 84 flows through the filter 66 into the resistance 61. The resulting potential across resistance 6! is in such a direction as to oppose the potential applied to the tip and ring of the line circuit by the subscribers cord. This releases tube T600. When tube T7 operates, alternating potential is applied to the grid of tube Ta through transformers 65 and. 69. The tube T8 is held normally released by the negative potential supplied by battery 1B. When tube Ta operates, it applies a relatively low impedance across the tip and ring of the two-wire recording trunk through the antiresonant circuits II. The placing of this low impedance across the tip and ring conductors of the recording trunk will allow current to flow from battery 45 through a resistance in the local A operators cord circuit similar to resistance 42, which in a manner similar to that described with respect to resistance 42 will apply a potential to tube Ts so as to extinguish or release it. These anti-resonant circuits are placed in the leads to the trunk to prevent the alternating potential supplied to the tube by generator 12 through transformer 13 from being fed back into the trunk. When the toll operator has received the instructions concerning the call, she pulls down from the line jack 51. This removes battery 293 from the sleeve of the jack and thus removes the potential drop across resistance 60. Tube TI releases and removes the potential drop from across resistance 61 and also removes the voltage from the grid of tube Ts causing it to release. The removal of the potential drop across resistance 67 will cause tube T600 to operate at this time and it will remain operated until the jack is removed from plug 48. The release of tube T8 removes the low impedance from across the two-wire recording trunk. This gives a visual indication to the local operator to remove her plug from the line jack of the recording trunk. When the local operator removes the subscribers cord from the recording trunk, tube T600 is extinguished as referred to above.

The operation of tube T9 will now be described. When the local operator inserted the subscribers cord in the jack of the two-wire recording trunk, a positive potential was placed on the grid of tube T9, causing it to operate. Tube T9 is normally held released by the negative potential supplied by battery 14 through resistance 15. The plate potential of tube T9 is supplied by the generator 16 through transformer 11. When an alternating current flows in the plate circuit of call sheinserts plug I93 into the tube T9,an alternating-potential is applied to rectifier unit I9 by transformer- Ill. The unidirectional-current from rectifier I9 flows throughresistance 59- in such a direction as to oppose the flow of current caused by the battery 293 in to make the sleeve'circuit appear as a very high- -impedance circuit to the toll cord. Should the local operator remove the plug from jack 48 before the toll operator removes the plug from jack 5'I, tube T9 would be released, the counter voltage set up by the rectifier unit 19 would be removed, and the sleevecircuit-would appear as a low impedance circuit. visual signal at the toll operators positionin the toll cord circuit dueto the operation of tube-T42 as-hereinafter described. Anti-resonant circuits 80 are placedin'the input circuit of tube T9 to prevent the alternating potential supplied to the plate of that tube from feeding back into the two-wire recording trunk;

Figs. 6 and 7 illustrate "the-circuit of a toll :switching trunk which may be used if the outgoing call is to be completed over a through twoway'supervision toll line. When the toll operator plugs into line -jack 110, a potential drop of such a polarity is set up across resistance Ill that tube T24 operates. TubeTzi is held normally released by thepotential of battery 872. Alternating potential is applied to the plate of this tubeby generator 'l'I-3 through transformer I'M. The frequency ofthe alternating potential supplied bygenerator I13 is in the super-audible or carrier range; When tube T24 operates, a carrier frequency is sent out through transformer I15 and the carrier frequency filter I16 over the toll switching trunk to the terminal equipment at the local oifice shown in Fig. 6. The carrier frequency passes through the filters Ill and I18 and isapplied to the grid of tube T through transformer I19. TubeTzais held normally unoperated by the potential of the battery I80. When tube T25 operates, alternatingcurrent is caused to flow through primary I8I of. a three-winding transformer I82. Alternatingpotential from generator .I 83 is supplied to tube T25 through a threewinding transformer I84. An alternating po- 'tential applied to transformer. I82 from source 583 operates tube T26 in the following manner. Tube T26is normally held released by the negative potential of theibattery connected to its grid. The alternating potential applied to transformer 182 will because of rectifier I800 cause a potential.

to be applied across. resistance I80I in such a direction to overcome thenegative potential normally applied to the grid of tube T26 and will cause it to operate. Tube T26 is capable of giving a visual signal. When the local Bioperator sees the visual indication which results .from the operation of tube T26, she connects her headset to thetoll switching trunk by means of key I92. After ascertaining the proper destination of the proper line jack. This completes thesleeve circuit of plug I93, and battery I94 causes the potential drop across resistance I95to be in such a direction as to result in the operation of tube T22. This tube is normally held released by the negativepotential supplied by battery I9I5. The operation of tube T22 results in-the release of tube T26. This is because the alternating current in-the left hand primary winding of transformer 182. will oppose the aforementionedalternating :current in'the right hand This would cause a a winding of transformer I82 and the resulting'poe tential across resistance I80! will be zero thus permitting tube T26 to be released by the nega-. tive potential normally applied to its grid. When tube T22 operates, current flows through the pri-: mary. of transformer I9I. This results in a po-- tential being applied to rectifier I98,:which, in conjunction with filter I99, applies a unidirectional potential across resistance 200; This drop of potential is in such a direction as to cause the operation of tube T28 if the subscribers receiver is on the switch-hook. Tube 28 is normally held released by the potential supplied by battery 20 I.

Generator 203 supplies alternating potential of carrier frequency to the plate of this tube through transformer 1204. Anti-resonant circuit 202 in the input circuit of tube T28 prevents the alternating current from source 203' from being trans mitted into the talking circuit. When tube T22 operates, carrier frequency from generator "203 is sent through transformer 205 and filter 206 over the toll switching trunk to the toll end of the same.

This carrier frequency passes through filter 201 of Fig. '7 and causes the operation of tube T29 through transformer 208. When tubeTze operates, the resistance of the sleeve circuit of jack H0 is. changed from a high resistance to a low resistance thus causing a visual indication to be given to the toll operator by. the operationof tube T42 in the toll cord circuit .in a manner heretofore described. Tube Tze'was normally held unoperated by the potential of battery 209. Alternating potential from generator 2I0 is applied to the plate of the tube through transformer 2| I.

Returning to Fig. 6, if the subscribers receiver is off the switchhook which would bethenormal condition at this time for an outgoing call, current from battery 2I2 flows over the line through resistance 2I3. Thecurrent flows through resistance H3 in such a direction (namely in opposition to the currentthrough resistance 200) as to result infthe release of tllbeTze. When tube T22 releases,,the carrier frequency is removed from the line and tube T29 .of Fig 'l 'is therefore also released. This restores the high resistance sleeve circuit and extinguishes .the visual indication caused by tubeTh in the toll cord circuit. In other words if the subscribers receiver is off the hook the tube T43 in the tolloperators'cord .will not be operated at all at this time.

In the event that the toll operator should not be able at the moment to find an idle toll line, she might tell the subscriber .to hang up the receiver and await a call. When the toll operator desires to ring'the subscriber, she can do so by pulling her ringing key in the cord circuit of Fig.4; Thisapplies anegative potential to the tip of the .toll switching trunk, causing the operation of the tube T due to the drop in the resistance 2212. Tube T30 is normally held released -by the negative potential of battery 22l3'. Generator 2I5 supplies alternating potential of carrier frequency to the plate of tube T30 through transformer 2I6. Anti-resonant circuit 2 I4 isinserted in the input circuit of the tube to prevent thealternating potential applied tothe plate from and results in the release of tubes T32 and T33 and the operation of tube T31. identical in operation.

The anode circuits of tubes T32 and T33 are supplied with high frequency alternating current from the generator common to both through anode circuits and with direct current from battery 2I2. The frequency of this alternating current is above the range of speech frequencies used in telephony being, for example, 8,000 cycles if the transmission band for telephony ranges from 200 to 3,000 cycles. Anti-resonant circuits are provided to exclude this current from other portions of the trunk circuit. When arcs exist in each of these tubes T32 and T33, which will Tubes T32 and T33 are be during those portions of a. cycle when the anodes are positive with respect to their cathodes, if there is no input to transformers 220, current will flow in the anode-cathode path and speech current superposed thereon may flow from anode to cathode or vice versa, provided the amplitude of the current from the high frequency source exceeds that of the speech currents. These speech currents will modulate the 8,000 cycle current but only the speech frequencies will pass through the anti-resonant circuits associated with the alternating current anode supply to tubes T32 and T33. Thus a talking path is completed through the normally operated tubes T32 and T33. Direct current from battery 2 I 2 also flows through the anode-cathode path of tube T32 and the subscribers line when plug I93 is inserted in jack I4, thence through the induction coil 6 and transmitter 5, returning over the subscribers line, and by way of jack I4 and plug I93 to the anodecathode discharge path of tube T33, and thence through the repeating coil and resistance 2 I 3 and the negative pole of battery 2I2. Transmitter current modulated by the voice at transmitter 5 is thus supplied through the discharge paths of tubes T32 and T33, which paths are in series for this direct current flow. Superposed on this and producing interruptions at a frequency above the band used for speech transmission is the alternating current supply to tubes T32 and T33, which frequency passing through the transformers 220 and 22I effects the release of tubes T32 and T33 and the operation of tube T31 in the following manner:

Rectifier 223 and filter 224 convert the alternating current voltage from transformer 220 into a direct current and thereby bias the grid of tube T32 to a negative value such that the arc Will not restrike on the next positive half cycle of the high frequency alternating current anode supply. Thus the application of the carrier frequency to transformer 220 releases tube T32 and similarly tube T33. At the same time the grid of tube T31 is made positive due to the positive half cycles. The release of tubes T32 and T33 will open the trunk circuit so as to prevent the transmission of ringing current back to the toll operator by the operation of tube T31 as will now be described.

Tube T31 and the circuit associated with it functions in the following manner: The tube T31 is normally held released by the negative potential of battery 22 I4. The alternating potential apvents the carrier frequency heretofore referred to plied' through transformer 22I will cause the tube to operate. When the tube is operated ringing current from source 22I5 will be applied to the line and to the subscribers line.

A description will now be given of the circuits of the equipment included at the terminals of a through two-way supervision toll line. As stated above, all supervisory signals of this type of system are transferred directly-to the outward toll operator. On-hook signals from either the calling or the called subscriber appear as visual signals in the outward toll operators cord circuit. If the call is to be passed over more than one through two-way supervision toll line, the intermediate toll operator must select the through jack instead of the outward jack. When this jack is selected, all on and off-hook signals are transmitted through the intermediate position without giving any visual signal at this position. However, the disconnect signal does appear as a visual signal at the intermediate position. The distant toll operator is rung automatically in a through two-way supervision toll line.

Carrier frequencies are utilized for the control of supervisory signals, particularly in connection with on-hook and off-hook conditions and for other purposes, as has been heretofore described in connection with Figs. 6 and 7. These signals are transmitted continuously over the circuits while conversation is taking place, and so must lie outside, and preferably above, the audible range. These carrier frequencies are therefore of a different range from the voice frequency'carrier currents used on the toll line for signaling purposes, as will be hereinafter described. The superaudible carrier currents are utilized in the transmission of supervisory signals from one portion of the circuit to another over relatively short distances and will ordinarily be confined to a single office, or at the most over an interoifice trunk extending from one ofiice to another in the same service area. The voice frequency carrier currents used on the toll line for signaling purposes, as hereinafter described, are not applied during conversation, and currents lying in the voice frequency range may therefore be utilized for this purpose. In many cases the facilities used to interconnect the called and calling ends of the toll circuit would not transmit appreciably such superaudible frequencies. It is nevertheless desirable to prevent their transmission beyond the terminal equipment and low pass filters 5025 and 5025 cutting off above the voice frequency range in Figs. 11 and 11, respectively, are provided for this purpose. Similar filters might,if required, be included in the cord circuits of Fig. 6 or Fig. 8' adjacent to and in the tip and ring conductors of plug I93 of Fig. 6 or plug 244' of Fig. 8', or in the circuits tothe right of the district selector 5M3 of Fig. 5.

The through two-way supervision toll line equipment is so designed as to make use of a plurality of carrier frequencies in the voice frequency range each of which is modulated at various frequencies to carry supervisory signals from one toll terminal to the other. One carrier frequency may be used to transmit the signals from the outward to the inward end of the toll line while another carrier frequency may be used to transmit the signals from the inward to the outward end. Other such carrier frequencies might be utilized for other signals if desired. Each carrier that is used may be modulated at a plurality of frequencies for example, four. The

the second toll line.

moduiationfrequencies are used to transmit the outward-toll operators connect and'disconnect signals and the called subsoribers receiver onhook and off-hooksignals; The unmodulated carrier frequencies themselves may also be used for signaling purposes if desired. Each terminal is equipped with two ringers R1 and R2 shown in Fig. 11 and R1 and R'z shown in Fig. 11, which are tuned to the frequencies sent out by the outward and the inward terminals respectively. Ringer R1 is normally connected to the toll line through the directional selection circuit 1M. Ringer R2 is connected to thetoll line automatically when the terminal equipment is selected by an outward operator as will be pointed out here- I-Iereafter in the description of the inafter. through two-way supervision toll line circuit F1, F2, F3, F4 will be used to designate supervisory signals sent to indicate connect, disconnect, on-

"hook and off-hook conditions, respectively,-from the outward position. G1, G2, Gs'and G4 will be used to designate the'same signals sent from the inward position. Every signal which is sent out must receive an acknowledgment signal from *the distant end.

Figs. 9, l and 11 show certain details of the terminal circuit arrangements used by the outward toll operator to complete a toll callover the through two-way supervision toll line. Each 'end of a toll line of this type would terminate in an outward jack, a through jack, a plug and associated equipment. equipment may be termed outward terminal At the outward toll oifice only the outward and through jacks and their associated equipment are illustrated. The plug and its associated equipment would be identical with the plug and equipment shown in Fig. 12' at the inward end of the line. It would be associated with the toll line at theoutward position by being connected to condu'ctors Adi. It would also be connected to the circuits till, 3532, and 85d of ringer R1, shown '--'in Fig. 11 in the same manner that the plug and its associated equipment, shown in Fig. 12" is connected to the circuits of ringer R1 of Fig. 11.

With respect to the outward jack MW and the through jack E28 shown in Fig. 9,-it is. pointed out -'-that the outward jack would always be utilized at the originating end of the toll connection.

However, if the call is to be completed over a sec- 0nd toll line the plug at the end of thefirst toll line would be connected into the through jack of Such a through jack and its equipment is shown as jaclt 52's in Fig. 9. The

through jack and its associated equipment in'the second toll line used in a through connection 7 would be similar to this jack. At the distant-end ite only has been shown. However, in practice, a through jack would be provided and would have its equipment connected to the leadsil'25" and H3 in Fig. 9' in a manner similar to that shown.

in Fig- 9.. A more detailed description .ofthe through jack apparatus will be: given hereinafter.

In initiating a call the outward itoll operator will insert the plug of a toll cord in the line jack dill) of the toll line. As will be pointedout muetail hereinafter this operation sends asignal to the distant toll operator at the inward position.

linevand connects the ringer R2. to the line.

The jacks and associated-- of the toll line shown inFig. 9 the outward jack also prepares the sleeve circuit of the toll operators cord to receive supervisory signals from the called subscriber. Adetailed description of these operations will now be given.

When the plug of the toll cord is inserted in jack 4% of'Fig- 9 potential from battery 29! is supplied to the sleeve circuit and the resulting potentialdrop across resistance 40! is of such a value and polarity as to cause tube T55 to operate. This tube is normally held released by the negative'potential of battery M2 applied to the grid. 1 Generator 4G3 supplies the plate potential through transformerdfi l. When tube T55 operates, alternating cur-ent is supplied through transformer 485 to circuit 4% which is connected to the ringer circuits shown on Fig. 11 and t0- the circuits of tubes T55, T57, T58, T59 and T50. shown in Fig. 9.

Tubes T55 and. T57 are normally operated and connect the plug and its associated equipment heretofore'refered to, to the toll line. As pointed out this i plug and its associated equipment is connected to circuit 401; When alternating current is supplied to the circuit of these tubes. by

transformer 485 through transformers M8, the tubes release thus removing .the plug. and its associated equipment from the toll line. Nor.- mally there is an are between the anode and cathode of tubes T56 and T5'1, the current being supplied from the battery Hill, the negative pole thetransmission circuit, and inductances 188" and I89 interconnect the collectors of the tubes T55 :andiTsi. The center-tap of eachof these inductances is connected to a tap on the resistance 733 or 7184 in' the individual anode circuit ofi'each of. these tubes, whereby the collectors areheld at'a potentialslightly positivewith re-' spect to the anode of each tube. This results in a .low'impedance in'tthe circuit collector-cathode-collectorof: each of these tubes. When alternating "potential is supplied through transformers 465- and ll8 it is rectified by rectifiers Mid and after passing througha filter is applied to resistance l82'in the common portion of the anode circuit-of tubes T55 and T57. and produces a voltage drop therein which is opposite to the polarityofwbattery .780, so that the anodes and collectors -of the tubes T and T57 are madenegative with respect to the cathodes thereof, extinguishing the arc and creating a substantiallyv open circuit condition between the collectors of each tube. The inductances E88 and 759 between the collectors of tubes T55 and T57 are of such a value that their inductive reactance at voice frequency is very high so that the circuit isefiectively open for such frequencies. It may also be noted that the inductance 18! between-the cathodes of the tubes T55 and T57 is of-sucha value that its inductive reactance, which is-..inshunt to the transmission circuit when .these tubes are in the conducting condi.

tion; is so high *as' to occasion but a negligible transmission loss;

Tube T55 ofFigrzQ isthe tubewhich causes the signal to be sent to the distant end of the toll line indicating to the toll operator that a call is waiting on that toll line. When alternating current is applied to the grid circuit of tube T58 by transformer 455 through transformer 409, a unidirectional potential of the proper value and polarity is applied to the grid of the tube to cause it to operate. The operating potential of tube T58 is supplied across resistance M2 by the rectifier 4 l 9 working through filter 4| I. This tube is normally held released by the negative potential of battery M3 applied to the grid. Generator 4| 5 supplies the plate potential of the tube through transformer M6. When tube T58 operates alternating current is supplied to circuit M8 by transformer 411. The alternating current in circuit 4|8 causes a signal voltage F1 to be sent out over the toll line. This is accomplished by the equipment I30! shown in detail in Fig. 10 which will be described at a later time.

When signal F1 arrives at the distant toll terminal, it produces a visual indication in front of the inward toll operator and also sends back to the outward end an acknowledgment signal G1. The details of these operations will be described hereinafter. This signal G1 is received and detected by ringer R2 of Fig. 11. It will be the type of signal which will be selected by cir cuit 95L An alternating current is thus produced in circuit 419 of Fig. 9. This alternating current is applied to the grid of tube T59 through transformer 420. This tube is held released normally by the negative potential of battery 42! applied to the grid. The plate potential of the tube is obtained by the resistance drop across resistance 424. This unidirectional potential across resistance 424 is supplied by rectifier 423 which obtains an alternating potential from transformer 422. Condenser 425 is of such a value as to prevent the release of the tube T59 during the short interval when the toll operator is throwing her talking key from the normal to the talking position.

The operation of tube T59 of Fig. 9 causes a flow of current through resistance 4l4 of such a value and polarity as to result in the release of tube T58. This removes signal voltage F1 from the line. The removal of signal voltage F1 from the line in turn removes the signal voltage G1 from the line, as will be explained hereinafter.

When the distant called subscribers line is reached in a manner to be pointed out herein after and the subscriber removes the receiver from the switchhook a signal of frequency G4 is received by ringer R2 of Fig. 11. The manner in which this operation is accomplished will be explained hereinafter. This signal G4 would be the type selected by circuit 904 of ringer R2. This causes an alternating current to be set up in circuit 426 of Fig. 9 and causes a signal F4 to be returned to the inward end where it removes signal G4. The manner in which the signal F4 is returned to the inward end of the line in order to remove the signal G4 is as follows: Connected in parallel with circuit 426 is a circuit, shown in Fig. 10, leading to the input of signaling equipment I394. The received signal G4 will traverse this path and in a manner to be pointed out later will cause the signaling equipment [304 to transmit back over the signal F4. This in a manner to be described later will remove signal G4 from the line. The removal of signal G4 automatically removes the signal F4 from the line. This alternating current of signal G4 is applied through transformer 42! to the slow-release and slow-operate circuit of tube T61 of Fig. 9. The slow-operate and release circuit of the tube is comprised of resistances 429 and 430, rectifier 428 and condenser 43]. This tube is normally held released by the negative potential of battery 432 applied to the grid through resistance 433. The plate potential of the tube T61 is supplied by battery 434. The operation of tube T61 from the pulse of signaling current G4 results in the flow of alternating current through the primary winding of transformer 435. The source of the alternating current is generator 436 which is supplied to the plate circuit through transformer 431. The tube T61 will not release at this time when G4 ceases because the normal potential of battery 434 is sufiicient to maintain it operated once it has been operated.

The operation of tube T61 causes tube T62 to release. Tube T62 is held normally operated by the positive potential of battery 438.

Battery 293 on Fig. 4 is connected with its positive pole grounded and its negative pole is connected through resistance 28'! and the contacts of key 288 to the sleeve circuit of jack 455 when plug of the toll cord is inserted therein. In this manner the positive grounded battery 293 supplies voltage to the anode circuit of tube T62, which is shown grounded through resistance 443. Thus, as tube T62 is normally operated, the sleeve circuit is completed to ground through the high resistance 444 and in parallel therewith through the anode-cathode discharge path of tube T62, and through the winding of transformer 435 and the low resistance 443. The resulting effective resistance therefore of the sleeve circuit Will be approximately that of resistance 443, and so relatively low.

When alternating current flows through transformers 435 and 431 due to the operation of tube T61 the rectifier and filter circuit associated with transformer 431 change the bias of the grid of tube T62 to a negative value, so that when the alternating voltage appearing across the secondary of transformer 435 reduces the anode current in T62 to zero, the grid thereof regains control and T62 is released. When this tube is released resistance 443 is effectively replaced by resistance 444 in the sleeve circuit jack 400. Resistance 444 is a high resistance and therefore extinguishes the lamp in the toll operators cord circuit. This indicates to the tool operator that the subscriber has answered the call. Tube T44 in the toll operators cord circuit was originally operated when a connection was made with jack 400 because the sleeve circuit of the toll cord was completed through the low resistance 443 and tube T62.

When the subscriber has completed the call and replaces the receiver on the switchhook a signal G3 is sent over the toll line and received by ringer R2 of Fig. 11. This applies an alternating current to circuit 459 and sends back a signal F3 to the inward end where G3 is then removed. The manner in which signal G3 causes a signal F3 to be sent back over the line is similar tothat described respecting G4 and F4. Signal G3 causes the operation of apparatus I303 and this sends signal F3 back over the line. Signal F3 will then remove signal G3 as pointed out hereinafter. Tube T63 of Fig. 9 is caused to operate by the application of this alternating current through transformer 45l to the slowoperate, slow-release circuit in the grid of the tube. This circuit is comprised of resistances 

